We have studied the components of the hormone receptor-adenylate cyclase complex. The turkey erythrocyte, a readily available, homogeneous cell type has been used as a model system. The turkey RBC plasma membrane possesses beta-adrenergic receptors identified using radioiodinated hydroxybenzylpindolol, a high-affinity beta-blocker. Beta receptors are coupled to adenylate cyclase catalytic units by a guanine nucleotide binding protein (G-unit) which we have isolated by affinity chromatography. We have studied the role of the G unit in mediating activation of adenylate cyclase by hormone, fluoride and cholera toxin. Beta-adrenergic agonist stimulation of cAMP accumulation in turkey erythrocytes leads to significant changes in sodium and potassium transport.